Bioinspired magnetite synthesis via solid precursor phases

Understanding microbial biomineralization at the molecular level: recent advances

Microbial biomineralization is a phenomenon involving deposition of inorganic minerals inside or around microbial cells as a direct consequence of biogeochemical cycling. The microbial metabolic processes often create environmental conditions conducive for the precipitation of silicate, carbonate or phosphate, ferrate forms of ubiquitous inorganic ions. Till date the fundamental mechanisms underpinning two of the major types of microbial biomineralization such as, microbially controlled and microbially induced remains poorly understood. While microbially-controlled mineralization (MCM) depends entirely on the genetic makeup of the cell, microbially-induced mineralization (MIM) is dependent on factors such as cell morphology, cell surface structures and extracellular polymeric substances (EPS). In recent years, the organic template-mediated nucleation of inorganic minerals has been considered as an underlying mechanism based on the principles of solid-state bioinorganic chemistry. The present review thus attempts to provide a comprehensive and critical overview on the recent progress in holistic understanding of both MCM and MIM, which involves, organic-inorganic biomolecular interactions that lead to template formation, biomineral nucleation and crystallization. Also, the operation of specific metabolic pathways and molecular operons in directing microbial biomineralization have been discussed. Unravelling these molecular mechanisms of biomineralization can help in the biomimetic synthesis of minerals for potential therapeutic applications, and facilitating the engineering of microorganisms for commercial production of biominerals.

Elucidating the Bioinspired Synthesis Process of Magnetosomes-Like Fe3O4 Nanoparticles

Iron oxide nanoparticles are a kind of important biomedical nanomaterials. Although their industrial-scale production can be realized by the conventional coprecipitation method, the controllability of their size and morphology remains a huge challenge. In this study, a kind of synthetic polypeptide Mms6-28 which mimics the magnetosome protein Mms6 is used for the bioinspired synthesis of Fe3O4 nanoparticles (NPs). Magnetosomes-like Fe3O4 NPs with uniform size, cubooctahedral shape, and smooth crystal surfaces are synthesized via a partial oxidation process. The Mms6-28 polypeptides play an important role by binding with iron ions and forming nucleation templates and are also preferably attached to the [100] and [111] crystal planes to induce the formation of uniform cubooctahedral Fe3O4 NPs. The continuous release and oxidation of Fe2+ from pre-formed Fe2+-rich precursors within the Mms6-28-based template make the reaction much controllable. The study affords new insights into the bioinspired- and bio-synthesis mechanism of magnetosomes.

Biocatalysis as a Green Approach for Synthesis of Iron Nanoparticles—Batch and Microflow Process Comparison

There is a growing need for production of iron particles due to their possible use in numerous systems (e.g., electrical, magnetic, catalytic, biological and others). Although severe reaction conditions and heavy solvents are frequently used in production of nanoparticles, green synthesis has arisen as an eco-friendly method that uses biological catalysts. Various precursors are combined with biological material (such as enzymes, herbal extracts, biomass, bacteria or yeasts) that contain chemicals from the main or secondary metabolism that can function as catalysts for production of nanoparticles. In this work, batch (“one-pot”) biosynthesis of iron nanoparticles is reviewed, as well as the possibilities of using microfluidic systems for continuous biosynthesis of iron nanoparticles, which could overcome the limitations of batch synthesis.

Carbon dots decorated magnetite nanocomposite obtained using yerba mate useful for remediation of textile wastewater through a photo-Fenton treatment: Ilex paraguariensis as a platform of environmental interest-part 2

Two carbon dots (CD) with diameters of 4.9 ± 1.5 and 4.1 ± 1.2 nm were successfully synthesized through an acid ablation route with HNO₃ or H₂SO₄, respectively, using Ilex paraguariensis as raw material. The CD were used to produce magnetite-containing nanocomposites through two different routes: hydrothermal and in situ. A thorough characterization of the particles by transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), dynamic light scattering (DLS), Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) indicates that all nanomaterials have spherical-like morphology with a core-shell structure. The composition of this structure depends on the route used: with the hydrothermal route, the shell is composed of the CD, but with the in situ process, the CD act as nucleation centers, and so the iron oxide domains are in the shell. Regarding the photocatalytic mechanism for the degradation of methyl orange, the interaction between the CD and the magnetite plays an important role in the photo-Fenton reaction at pH 6.2, in which ligand-to-metal charge transfer processes (LTMCT) allow Fe²⁺ regeneration. All materials (100 ppm) showed catalytic activity in the elimination of methyl orange (8.5 ppm), achieving discoloration of up to 98% under visible irradiation over 400 nm in 7 h. This opens very interesting possibilities for the use of agro-industrial residues for sustainable synthesis of catalytic nanomaterials, and the role of the interaction of iron-based catalysts with organic matter in heterogeneous Fenton-based processes.

Sustainable utilization of water treatment residue as a porous geopolymer for iron and manganese removals from groundwater

Raw water is a significant resource for industrial water usage, but this water is not directly suitable for use due to the presence of contaminants. Therefore, pre-treatment is essential. The treatment generates water treatment residue (WTR) which consists of silt, clay and undesirable components. Most WTR is conventionally disposed of in landfill. In addition, the presence of iron (Fe) and manganese (Mn) in groundwater can result in a reddish-brown color and undesirable taste and odour. A number of expensive and complex technologies are being used for the removal of such iron and manganese. Due to the high Al₂O₃ and SiO₂ content in WTR, therefore, this research proposes the use of WTR as the source material for geopolymer production for Fe/Mn removal. With the availability of free alkali in the geopolymer framework, the OH^--releasing behavior of the WTR-based geopolymer was investigated by the precipitation of Fe(II) ion. The WTR-based geopolymer was calcined at 400 °C and 600 °C to obtain a strong geopolymer matrix with the ability to remove Fe/Mn ions. The results show that the WTR-based geopolymer has the potential to remove Fe from Fe-contaminated water. Hydroxide ions are released from the geopolymer and form an Fe(OH)₃ precipitate. Geopolymer with a calcination temperature of 400 °C provides total removal of the Fe after 24 h of immersion. In addition, the existence of Fe(OH)₃ helps to coprecipitate the Mn(OH)₂ in the Fe/Mn solution leading to a significant reduction of Mn from the solution. The pH value and retention time play an important role in the final metal concentration. The final pH of the solution is close to 8.5, which is the recommended value for boiler water. This method offers an alternative use of WTR in making a porous geopolymer for groundwater Fe/Mn removal using a simple method.

The Deep Eutectic Solvent Precipitation Synthesis of Metastable Zn4V2O9

A precipitation method involving a deep eutectic solvent (DES)─a mixture of hydrogen bond donor and acceptor─is used to synthesize a ternary metal oxide. Without toxic reagents, precipitates consisting of Zn₃(OH)₂V₂O₇·nH₂O and Zn₅(OH)₆(CO₃)₂ are obtained by simply introducing deionized H₂O to the DES solution containing dissolved ZnO and V₂O₅. Manipulation of the synthetic conditions demonstrates high tunability in the size/morphology of the two-dimensional nanosheets precipitated during the dynamic equilibrium process. According to differential scanning calorimetry and high-temperature powder X-ray diffraction, Zn₃V₂O₈ and ZnO obtained by the annealing of the precipitate are intermediates in the reaction pathway toward metastable Zn₄V₂O₉. Intimate mixing of the metal precursors achieved by the precipitation method allows access to the metastable zinc-rich vanadate with unusually rapid heat treatment. The UV-vis and surface photovoltage spectra reveal the presence of sub-band gap states, stemming from the reduced vanadium (V⁴⁺) center. Photoelectrochemical measurements confirm weak photoanodic currents for water and methanol oxidation. For the first time, this work shows the synthesis of a metastable oxide with the DES-precipitation route and provides insight into the structure-property relationship of the zinc-rich vanadate.

Desulfovibrio Bacteria Are Associated With Parkinson's Disease

Parkinson's disease (PD) is the most prevalent movement disorder known and predominantly affects the elderly. It is a progressive neurodegenerative disease wherein α-synuclein, a neuronal protein, aggregates to form toxic structures in nerve cells. The cause of Parkinson's disease (PD) remains unknown. Intestinal dysfunction and changes in the gut microbiota, common symptoms of PD, are evidently linked to the pathogenesis of PD. Although a multitude of studies have investigated microbial etiologies of PD, the microbial role in disease progression remains unclear. Here, we show that Gram-negative sulfate-reducing bacteria of the genus Desulfovibrio may play a potential role in the development of PD. Conventional and quantitative real-time PCR analysis of feces from twenty PD patients and twenty healthy controls revealed that all PD patients harbored Desulfovibrio bacteria in their gut microbiota and these bacteria were present at higher levels in PD patients than in healthy controls. Additionally, the concentration of Desulfovibrio species correlated with the severity of PD. Desulfovibrio bacteria produce hydrogen sulfide and lipopolysaccharide, and several strains synthesize magnetite, all of which likely induce the oligomerization and aggregation of α-synuclein protein. The substances originating from Desulfovibrio bacteria likely take part in pathogenesis of PD. These findings may open new avenues for the treatment of PD and the identification of people at risk for developing PD.

In situ mechanical reinforcement of polymer hydrogels via metal-coordinated crosslink mineralization

Biological organic-inorganic materials remain a popular source of inspiration for bioinspired materials design and engineering. Inspired by the self-assembling metal-reinforced mussel holdfast threads, we tested if metal-coordinate polymer networks can be utilized as simple composite scaffolds for direct in situ crosslink mineralization. Starting with aqueous solutions of polymers end-functionalized with metal-coordinating ligands of catechol or histidine, here we show that inter-molecular metal-ion coordination complexes can serve as mineral nucleation sites, whereby significant mechanical reinforcement is achieved upon nanoscale particle growth directly at the metal-coordinate network crosslink sites.

Biological organic-inorganic materials, such as self-assembling metal-reinforced mussel holdfast threads, remain a popular source of inspiration for materials design and engineering. Here the authors show that metal-coordinate polymer networks can be utilized as simple composite scaffolds for direct in situ crosslink mineralization.

Green synthesis of copper oxide nanoparticles for biomedical application and environmental remediation

Recent development in nanoscience and nanotechnology has contributed to the wide applications of metal and metal oxides nanoparticles in several field of sciences, research institutes and industries. Among all metal oxides, copper oxide nanoparticles (CuONPs) has gained more attention due to its distinctive properties and applications. The high cost of reagents, equipment and environmental hazards associated with the physical and chemical methods of synthesizing CuONPs has been a major setback. In order to puffer solution to the aforementioned challenges by reducing environmental pollution and production of cheaper nanoparticles with good properties and efficiency, this review focus on collection of comprehensive information from recent developments in the synthesis, characterization and applications from previous scientific findings on biological method of synthesizing CuONPs due to the acclaimed advantages of been cheap, environmentally friendly, convenient and possibility of been scale up in into large scale production reported by numerous researchers. Our finding also support the synthesis of CuONPs from plant sources due to relative abundance of plants for the production of reducing and stabilizing agents required for CuONPs synthesis, potential efficiency of plant biomolecules in enhancing the toxicity effect of CuONPs against microbes, prevention of environmental pollution due of nontoxic chemicals and degradation effectiveness of CuONPs synthesized from plant sources. Furthermore, this study provide useful information on the rapid synthesis of CuONPs with desired properties from plant extracts.